CBS Local — Astronaut Scott Kelly set a record for the longest single spaceflight in history and now NASA is saying the trip made him a “new man” as well. A study of Kelly and his identical twin brother found that spending nearly a year in space significantly changed the astronaut’s DNA.
Kelly spent 340 straight days aboard the International Space Station from 2015 to 2016. When the NASA veteran returned to Earth, researchers immediately noted that he had grown two inches in height. A new study comparing Scott to his identical twin, Mark — who is also a NASA astronaut and stayed on Earth during the 340-day trip — has revealed that long-term space travel alters more than just your height.
“Scott’s telomeres (endcaps of chromosomes that shorten as one ages) actually became significantly longer in space,” NASA researchers wrote in a statement . The space agency added that Kelly had hundreds of “space genes” activated by the year-long flight which reportedly altered the astronaut’s “immune system, DNA repair, bone formation networks, hypoxia, and hypercapnia.”
While Scott Kelly’s height and 93 percent of his DNA returned to normal after returning to Earth, NASA confirmed that seven percent of his genes have remained changed and may stay that way. “This is thought to be from the stresses of space travel, which can cause changes in a cell’s biological pathways and ejection of DNA and RNA,” researchers added .

What? My DNA changed by 7%! Who knew? I just learned about it in this article. This could be good news! I no longer have to call @ShuttleCDRKelly my identical twin brother anymore. https://t.co/6idMFtu7l5
— Scott Kelly (@StationCDRKelly) March 10, 2018

NASA also found that Kelly’s mental reflexes and accuracy dropped off significantly after coming back to Earth. The mental slow down was blamed on “re-exposure and adjustment to Earth’s gravity.”